Mosquitoes are currently the most important arthropod vectors, transmitting a broad range of diseases such as malaria, lymphatic filariasis and dengue fever. A method for curtailing disease transmission is through vector control programs. It has been shown that mosquitoes are able to mount powerful cellular and humoral responses against invading pathogens, and that this response is directly correlated to vector competence. To date, most studies addressing mosquito immunity have focused on the humoral response. However, it is clear that hemocytes (mosquito blood cells) play a central role in the production of many of the players involved in the humoral response. The current study will address the role hemocytes from two immunologically different mosquito species, Aedes egypti and Armigeres subalbatus, have in the immune response mounted against prokaryotic, protozoan and metazoan parasites. This research will focus on 1) classifying the hemocytes, 2) studying the phagocytic response of hemocytes towards pathogens, 3) determining which cells are responsible for the transcription of immune molecules, and 4) determining the structure/function relationship between invading pathogens, hemocytes and soluble immune molecules. In understanding the immune response mounted by different insect species and strains toward pathogens, it may be possible to manipulate existing vectors to make the parasite/vector biologic interplay incompatible.